The present disclosure relates to a conveyance unit preferably applied in a copying machine or a printer or the like and an image forming apparatus including this.
An image forming apparatus such as a copier and a printer includes a conveyance unit bringing an uppermost sheet of a stacked sheet bundle into pressure contact with a sheet feed roller to convey the sheet.
For instance, a sheet feed unit (a conveyance unit) includes a lift plate provided liftably within a sheet feed cassette, a coil spring for biasing the lift plate upward, and a hook-like eccentric cam for pressing down the lift plate by resisting against a bias force of the coil spring. The eccentric cam is fixed to a shaft and is rotationally driven in one direction. The eccentric cam controls the lift of the lift plate by coming in sliding contact with a cam follower attached to the lift plate. When no sheet is fed, the eccentric cam is located at a reference position and pushes down the lift plate to a vicinity of a lowest point.
However, the conveyance unit described causes the following trouble in attaching the sheet feed cassette. That is, when the sheet feed cassette is drawn out of the apparatus body to replenish sheets for example, the eccentric cam is disengaged from the cam follower and turns in one direction from the reference position. When the sheet feed cassette is attached in this state, the cam follower pushes out the eccentric cam in a cassette attachment direction without engaging with the eccentric cam. Therefore, the eccentric cam of the conveyance unit described above is unable to press down the lift plate. In such a case, it has been required to rotate the eccentric cam once to engage with the cam follower to press down the lift plate. That is, the conveyance unit described above has a problem that it requires to consume a wasteful time and energy of returning the eccentric cam to the reference position.